This invention relates to valve gated injection molding and more particularly to an improved system in which the heated nozzle has a nose portion which extends through an opening in the cavity plate directly to the cavity and itself forms the gate in which the tip end of the valve pin seats to control the flow of melt to the cavity.
As is well known in the art, this type of injection molding sytem has an insulative air space extending between the heated nozzle and the cooled cavity plate. In many early applications, this space was allowed to fill with melt which partially solidified and acted as an insulator. However, this has the disadvantage that it is difficult, if not impossible, to clear the previous material on colour and/or material changes, and furthermore for some materials additional heat is required in the gate area to ensure satisfactory seating of the valve pin in the gate.
Thus, in order to overcome these problems, the applicant provided a hollow cylindrical nozzle seal formed of titanium as described in the applicant's U.S. Pat. No. 4,043,740 which issued Aug. 23, 1977. This seal is seated in both the nozzle and cavity plate to bridge the air space around the gate. More recently, as described in the applicant's U.S. Pat. No. 4,286,941 which issued Sept. 1, 1981, a titanium nozzle seal has been provided which extends through an opening in the cavity plate right into the cavity to provide even more heat in the gate area adjacent the cavity. While these previous systems have been very successful, they have the disadvantages that a particular unit has to be used for a particular gate size and the moldmaker has to be very precise in making the gate the correct size and the correct angle.
In a more recent application relating to a different aspect of sprue gating, the applicant discloses in Canadian patent application Ser. No. 370,734 filed Feb. 12, 1981 entitled "Heated Nozzle Bushing with Fixed Spiral Blade", a heated nozzle or nozzle bushing with a portion which extends through the cavity plate to the cavity. However, this structure was necessary to extend the spiral blade right to the cavity, and there is no suggestion it could be transposed to a valve gated system requiring a gate to seat the valve pin in.